1. Field of the Invention
The present invention generally relates to methods and circuits for power management, and in particular, to methods and circuits for power management in network transceivers.
2. Description of the Prior Art
In a network, there are generally one or more servers connected to a number of client machines via one or more hubs (or repeaters) and or switches. In each one of these devices, there may be one or more transceivers. Each transceiver, if connected to another transceiver, communicates with that transceiver. For example, generally speaking, a server machine has a network card, and there is a transceiver on the network card. If the server is connected to a repeater, it would be connected to the repeater at one of its ports and there would be a transceiver at this port (and each port of the repeater) communicating with the server in accordance with established protocols.
The manner in which the transceivers communicate with each other in an Ethernet environment is dictated by IEEE 802.3u. In the specification, it is specifically provided that for a 10 mb (mega bit per second) transceiver, during idle period (when the transceiver is not connected to another transceiver), the transceiver is required to transmit an idle signal to signal the existence of a live transceiver. In this manner, if another transceiver is connected to this transceiver, the two transceivers will detect the existence of each other and initiate communication protocol and transmit and receive data. FIG. 1a illustrates the industry standard specified normal link pulse (“nlp”) for transmission in the 10 mb mode. Note that there is a single pulse 10 every 16 ms. For 10 mb auto negotiation mode, referring to FIG. 1b, the industry specification requires that there be pulses separated by 16 ms intervals and each pulse 12 having a duration greater than a predefined duration. For 100 mb transceivers, referring to FIG. 1c, the signal type MLT3 having 3 levels of signaling is used.
While the industry specifications provide the idle signal type for each mode of operation, for 10/100 mb transceivers, the MLT3 type idle signal is specified. The disadvantage with this specification is that the MLT3 signal consumers a high amount of energy even when there is no activity. It increases power consumption and requires higher cooling requirement—all results in higher system cost.
There is much advantage that can be had if the power consumption level of the transceiver can be minimized. For example, if a repeater uses transceivers with low power consumption, the repeater may be designed without the use of a mechanical cooling fan. The lack of a cooling fan translates to lower overall system cost and higher system reliability (there is not a fan to fail). For the 10/100 mb transceivers, there are many opportunities for power savings if the circuits is designed to minimize power use.
Therefore, it is desirable to have a transceiver device with low power consumption.